Noise-shaping circuit, digital-to-time converter, analog-to-digital converter, digital-to-analog converter frequency synthesizer, transmitter, receiver, transceiver, method for shaping noise in an input signal

ABSTRACT

A noise shaping circuit according to an example includes a forward signal path configured to generate an output signal based on an input signal, a feedback signal path configured to feed back a feedback signal based on the output signal to the forward signal path, and a dither generator configured to generate a dither signal and to couple the dither signal into the forward signal path to modify the input signal and into the feedback signal path. Employing a noise shaping circuit according to an example may improve an overall noise performance.

REFERENCE TO RELATED APPLICATION

This application claims priority to German Application number 10 2014119 480.2 filed on Dec. 23, 2014, the contents of which are incorporatedby reference in their entirety.

FIELD

The present disclosure relates to a noise-shaping circuit, adigital-to-time converter, an analog-to-digital converter, adigital-to-analog converter, a frequency synthesizer, a transmitter, areceiver, a transceiver, a method for shaping noise in an input signaland corresponding computer-related implementations.

BACKGROUND

In many applications, noise-shaping techniques are used to increase anapparent signal-to-noise ratio in a frequency range. Examples come frommany fields of technology, for instance fields comprising digital orother quantized signal processing.

For instance, in many transmitter, receiver or transceiver applications,one or more local oscillator (LO) signals are used for up-mixing ordown-mixing a signal to be transmitted or received, respectively. Toreduce distortions more and more frequency synthesizers based on digitalphase-locked loops (DPLLs) have become an important approach becausethey may allow a greater flexibility and an easier configurability forcreating multiple local oscillator signals for multiple bands.

In this field, digital-to-time converters (DTCs) are becoming a more andmore attractive approach for the generation of local oscillator signalsin multi-standard radio-frequency (RF) transmitters, receivers ortransceivers as they may benefit from the digital design flow includingthe possibility of RF synthesis. To name just one example, DTC-basedtransceiver architectures may be used in protocols, where carrieraggregation (CA) is used and where multiple local oscillator signals mayhave to be generated by a single radio frequency DPLL driving multipleDTCs. Such a DPLL- and/or DTC-based frequency synthesizer may allow amore robust operation with respect to distortions and a higherintegration.

However, a DTC often quantizes with a finite number of levels, which mayresult in visible spurs in the spectrum. Moreover, in a digital DTC alsothe number of bits available may limit the spectral performance. Tofulfill certain spectral requirements imposed, for instance, by theapplication, the protocol to be used or other implementation details,noise-shaping techniques may be used. However, conventionalnoise-shaping techniques may negatively influence the spectral responseof such a system, for instance, at specific sensitive frequencies orfrequency bands.

Therefore, a challenge exists to improve an overall noise performance ofsuch a system.

However, not only in the field of transmitters, receivers ortransceivers, similar challenges exist. They exist in many fields ofsignal processing, for instance, comprises digital audio processing,digital image processing, digital video processing, analog/digitalconversion and similar technical applications and fields.

SUMMARY

Therefore, a demand exists to improve an overall noise performance of asystem employing noise-shaping techniques is a demand widely met in manyfields of technology.

This demand may be satisfied by a noise-shaping circuit, adigital-to-time converter, a frequency synthesizer, a transmitter, areceiver, a transceiver, a method for shaping noise in an input signalor corresponding software-related implementations according to any ofthe independent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Some examples of circuits, apparatuses and/or methods will be describedin the following by way of example only. In this context, reference willbe made to the accompanying Figures.

FIG. 1 shows a block diagram of a digital-to-time converter according toan example comprising a noise-shaping circuit according to an example;

FIG. 2 shows a comparison of noise spectra using a noise-shaping circuitaccording to an example;

FIG. 3 shows a block diagram of a possible implementation of a dithergenerator used in a noise-shaping circuit according to an example;

FIG. 4 shows a block diagram of a frequency synthesizer according to anexample;

FIG. 5 shows a block diagram of a transmitter, a receiver or atransceiver according to an example;

FIG. 6 shows a block diagram of an analog-to-digital converter accordingto an example;

FIG. 7 shows a block diagram of a digital-to-analog converter accordingto an example;

FIG. 8 shows a flowchart of a method for shaping noise in an inputsignal according to an example.

DETAILED DESCRIPTION

Various examples will now be described more fully with reference to theaccompanying drawings in which some examples are illustrated. In thefigures, the thicknesses of lines, layers and/or regions may beexaggerated for clarity.

Accordingly, while examples are capable of various modifications andalternative forms, the illustrative examples in the figures and willherein be described in detail. It should be understood, however, thatthere is no intent to limit examples to the particular forms disclosed,but on the contrary, examples are to cover all modifications,equivalents, and alternatives falling within the scope of thedisclosure. Like numbers refer to like or similar elements throughoutthe description of the figures. Moreover, summarizing reference signswill be used to refer to more than one structure, element or object orto describe more than one structure, element or object at the same time.Objects, structures and elements referred to by the same, a similar or asummarizing reference sign may be identically implemented. However, one,some or all properties, features and dimensions may also vary fromelement to element.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Other words used to describe therelationship between elements should be interpreted in a like fashion(e.g., “between” versus “directly between,” “adjacent” versus “directlyadjacent,” etc.).

The terminology used herein is for the purpose of describing particularexamples only and is not intended to be limiting of examples. As usedherein, the singular forms “a,” “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, integers, steps, operations, elementsand/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which examples belong. It will befurther understood that terms, e.g., those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

As briefly outlined before, in many fields of application noise-shapingtechniques may be used to improve an apparent signal-to-noise ratio insome frequency bands. Examples come from many fields of technology, inwhich signals are to be processed. For instance, by using noise-shapingtechniques it may be possible to influence the noise spectrum in such away that a noise level in a more relevant frequency range may bereduced, while a noise level in a less important frequency range isincreased. In some applications it may be possible to use filteringtechniques to reduce the noise created in the less important frequencybands, when, for instance, the respective frequency band is sufficientlyfar away from the more relevant frequency band and it is not usedapplication-wise, for instance, to transmit signals, to receive signals,to name just some examples.

However, in many fields of technology simply employing conventionalnoise-shaping techniques cannot be easily implemented since thesenoise-shaping techniques rely on dithering techniques which mayintroduce additional noise to the signal to be processed. As aconsequence, the additional noise caused by the dithering may violatespectral requirements imposed by the application, a protocol or otherimplementation details.

Examples come essentially from all fields of technology, in whichsignals are to be processed and/or quantized. For instance digital audioprocessing, digital image processing and digital video processing arejust some fields, in which noise-shaping techniques are employed. Aswill be laid out in more detail below, also in other fields oftechnology noise-shaping techniques can be employed.

Below, two examples will be shown in more detail, in which anoise-shaping circuit or corresponding noise-shaping techniques can beused. One example comes from the field of transmitters, receivers ortransceivers comprising a frequency synthesizer employing one or moredigital-to-time converters (DTCs). Another example comes from the fieldof analog-to-digital converters. However, a noise-shaping circuitaccording to an example as well as other examples including, forinstance, a method for shaping noise in an input signal andcorresponding software-related implementations described below canequally well be employed in other fields of technology. Hence, theexamples outlined below simply represent some examples, in which thenoise-shaping technique described below can be employed.

The first example comes from the field of transmitters, receivers andtransceivers to transmit and/or receive signals, which may, forinstance, comprise data. While a transmitter is designed to generate asignal and, optionally, to transmit the signal, a receiver is designedto receive appropriate signals. A transceiver is a circuit or device,which is capable of both transmitting and receiving signals. Atransceiver may, for instance, comprise dedicated transmitter andreceiver circuits, but may also comprise components or circuits whichmay be used for both, transmitting and receiving corresponding signals.

Although in the description below the signals will be mainly radiofrequency signals transmitted, for instance, by radio, the transmitters,receivers and transceivers are by far not limited to employingradio-based transmission technology. For instance, also cable-boundtransmissions as well as different frequencies above or below thesefrequencies may be used to transmit and/or to receive data. Moreover,instead of electric-based transmission schemes, which also includeradio-based transmission schemes, also other transmission schemes may beused including, for instance, optical transmission schemes and magnetictransmission schemes to name just some examples.

Moreover, in the following mainly digital processing circuits will bedescribed, in which a signal is sampled and quantized. In other words,in the following examples mainly digital signals will be described.However, it is by far not required to employ only digital signals, whichare quantized in terms of the time (sampling) and in terms of the valuethey may acquire (quantization). In other examples, non-digital signalsmay be used in which at least one of time, the values or both are by farnot required to be discrete. In the case of a signal having a continuousrange or spectrum of values and being continuous in terms of time, sucha signal is often referred to as an analog signal. In general, examplesmay also comprise corresponding analog or other non-digitalimplementations.

As briefly mentioned before, for transmitters, receivers andtransceivers, digital-to-time converters (DTCs) may represent anattractive solution for the generation of one or more local oscillator(LO) signals in the multi-standard radio frequency (RF) transceiverenvironment. These systems may benefit from the digital design flowincluding the possibility of radio-frequency synthesis. DTCs may beparticularly interesting in transmitters, receivers and transceiverssupporting, for instance, downlink carrier aggregation (CA), in whichmultiple local oscillator signals are used to increase an overalltransmission bandwidth. For instance, the multiple local oscillatorsignals may be generated by a single reference oscillator circuitcomprising, for instance, a radio frequency digital phase-locked loop(RF DPLL), which drives multiple digital-to-time converters. Such asolution may save not only chip area, but may also avoid magneticcoupling issues, which may occur in from multi-DPLL solutions.

Generally speaking, a DTC delays an edge of an oscillating signalprovided to an input of the DTC according to a control signal comprisinga code word provided to a control input of the DTC. The desired localoscillator frequency can therefore be obtained by applying, forinstance, a code ramp.

However, a DTC typically quantizes its delay of the oscillating signalprovided at the input of the DTC according to a finite number of levels.This quantization may produce visible spurs in the spectrum of the DTC.Moreover, the number of bits of a digital DTC may also limit thespectral performance. Noise-shaping may be used to lower a quantizationnoise at specific frequencies in order to fulfill spectral requirements,for instance, at the so-called duplex distance. The duplex distanceoften refers to a frequency distance between frequencies used foruploading and downloading data. In other words, the duplex distance mayrefer to a frequency distance between receiving and transmittingsignals. Depending on the standard and the technique involved, theduplex distance may be, for instance, in the range between 1 MHz andseveral 100 MHz.

As will be laid out in more detail below, examples employ additivedithering to remove, for instance, quantization spurs caused by the DTC.An example depicted in FIG. 2 and described below in more detail showsthat it may be possible to use a noise shaping technology includingdithering and still keep the spectral response introduced by the noiseshaper circuit and still remove or at least dampen the quantizationspurs. As a consequence, it may be possible to improve an overall noiseperformance of such a system.

Compared to a conventional approach, in an example of a noise-shapingcircuit a dither signal is applied to both a forward signal path and afeedback signal path. Such a dither signal or dither sequence cantherefore be used to smear quantization spurs. A straightforwardaddition will increase the power over all frequencies covering, forinstance, the frequency-dependent behavior of the noise shaper. However,to keep the frequency-dependent behavior, the dithering signal is notonly added to the forward signal path, but also the feedback loop or thefeedback signal path of the noise shaper.

Dithering, without also adding the dither signal to the feedback signalpath will very likely increase the spectral power independent of thefrequency and might therefore lead to a violation of spectralrequirements or error vector magnitude (EVM) targets laid out, forinstance, by standards, application requirements or implementationdetails.

A noise-shaping circuit as well as a method for shaping noise in aninput signal according to an example may be applied to many kinds ofnoise shaper for a systems based on quantizing and can also be used incombination with a non-linearity correction to name just a few examples.

FIG. 1 shows a block diagram of a digital-to-time converter 100 (DTC)comprising a digital-to-time converter circuit 110 (DTC circuit) as wellas a noise-shaping circuit 120, which is also referred to as a noiseshaper. The DTC circuit 110 is designed to generate a processedoscillating signal POS by delaying an oscillating signal OCS in responseto a modified control signal MCS. The modified control signal indicatesthe amount of delay applied by the DTC circuit 110.

The modified control signal MCS is here an output signal OS of thenoise-shaping circuit 120, the noise-shaping circuit 120 generates basedon a control signal CS received as an input signal IS. The noise-shapingcircuit 120 comprises a forward signal path 130 and a feedback signalpath 140. The forward signal path 130 is configured to generate theoutput signal OS, which corresponds in the example depicted in FIG. 1 tothe modified control signal MCS for the DTC circuit 110, based on theinput signal IS, which corresponds to the control signal CS. Thefeedback signal path 140 is configured to feed back a feedback signal FSbased on the output signal OS to the forward signal path 130. To allowthe feedback signal path 140 this, the feedback signal path 140comprises a noise-shaping filter 150, which is referred to in FIG. 1also by its filter function. The noise-shaping filter 150 generatesduring operation the feedback signal FS based on an error signal ES andprovides the same to the forward signal path 130. The error signal ESindicates a difference of the output signal OS with respect to anintended value thereof. The intended value may be based on a valuecomprised in the input signal IS. The intended value may be modified,for instance, by the feedback signal FS and/or a dither signal DS.

The noise shaping filter 150 generating based on the error signal ES thefeedback signal FS represents an example how the noise of the inputsignal IS may be shaped by providing the corresponding feedback signalFS back to the forward signal path 130. In principle, any suitablefilter function G(z) may be used in the framework of the noise-shapingfilter 150. For instance, both finite impulse response filters (FIRfilters) and infinite impulse response filters (IIR filters) may beused. In its simplest form, the filter function G(z) may correspond to asimple delay by one clock cycle (z⁻¹). However, by appropriatelyimplementing the noise-shaping filter 150 in principle any filterfunction may be implemented here.

The noise-shaping circuit 120 further comprises a dither generator 160which is configured to generate the dither signal DS and to couple thedither signal into the forward signal path 130 to modify the inputsignal IS and into the feedback signal path 140.

The dither generator 150 may be specifically designed to generate, forinstance, the dither signal DS comprising a white-noise spectraldensity. A white-noise spectral density is, under ideal circumstances,independent of the frequency or, in other words, constant as a functionof the frequency f. However, the dither generator 160 may equally wellbe designed to generate the dither signal DS having a pink-noisespectral density, which is proportional to the inverse of the frequencyf (proportional to 1/f=f⁻¹) or—in more general terms—proportional tof^(−α), where α is a number larger than 0, but smaller than 2. Often, αis close to 1 so that the pink-noise spectral density is roughlyproportional to the inverse of the frequency f.

The dither generator 160 may equally well be designed to generate aBrownian-noise spectral density, which is also referred to as ared-noise spectral density. The Brownian-noise spectral densitycorresponds to the noise produced by a Brownian motion and isapproximately inversely proportional to the square of the frequency f(i.e. approximately proportional to f^(−α) with a value a beingapproximately equal to 2). However, the dither generator 160 may equallywell be designed to produce the dither signal DS comprising a high-passfiltered white noise spectral density which may, for instance, beimplemented by differentiating a signal having a white-noise spectraldensity. Naturally, the dither generator 160 may equally well bedesigned to produce, for instance, depending on a dither input signalany of the previously-mentioned spectral densities of the dither signalDS. In principle, the dither generator 160 may be designed to producedifferent spectral densities for different frequency bands or ranges,for instance, depending on the previously-mentioned dither input signal.

In the example depicted in FIG. 1, the forward signal path 130 of thenoise-shaping circuit 120 comprises a signal processing circuit 170,which in turn is configured to generate the output signal OS based onthe input signal IS modified by the dither signal DS. The signalprocessing circuit which is referred to in FIG. 1 as “quantization” may,for instance, comprise a quantization circuit configured to modify avalue provided to the quantization circuit. For instance, the signalprocessing circuit 170 may be configured to re-quantize the signalprovided to the signal processing circuit 170. The signal processingcircuit may also be designed to reduce the number of different valuesthe output signal OS can acquire with respect to the number of differentvalues of the signal provided to the signal processing circuit 170. Forinstance, in the case of a digital implementation the signal processingcircuit 170 may truncate values, for instance, transmitting only aspecified number of most significant bits and truncating thecorresponding number of least significant bits. However, the signalprocessing circuit 170 may also be designed to at least partiallycompensate a non-linearity of a component coupled to the noise-shapingcircuit 120.

All these different examples may cause the output signal OS to deviatefrom an intended value. The intended value may correspond to a value ofthe input signal IS or a value changed, for instance, by thenoise-shaping filter 150 and, hence, by the feedback signal FS and/or bythe dither signal DS generated by the dither generator 160. As aconsequence, a deviation or difference of the output signal from thevalue comprised in the signal provided to the signal processing circuit170 occurs, which may then be provided to the noise-shaping filter 150in the form of the error signal ES to perform the noise shaping.However, irrespective of the actual implementation of the signalprocessing circuit 170, the signal processing circuit 170 causes adeviation of the quantization of the output signal OS with respect tothe signal provided through the signal processing circuit 170.

In the example depicted in FIG. 1, the signal processing circuit 170may, for instance, be configured to at least one of reducing the numberof different states of the output signal compared to the signal providedto the signal processing circuit 170 and compensating fully or at leastpartially a non-linearity of the DTC circuit 110.

The DTC 100 may be a fully digital DTC 100. As a consequence, also thenoise-shaping circuit 120 may be a digital noise-shaping circuit 120such that the forward signal path 130, the feedback signal path 140 andthe dither generator 160 may also be configured to receive, process andprovide signals comprising or indicating a sequence of digital values.In such an implementation, the signal processing circuit 170 may, forinstance, comprise a look-up-table to at least partially counteractnon-linearities of the DTC circuit 110. It may also truncate, forinstance, a specified number of least significant bits depending on thecapabilities of the DTC circuit 110 used.

To generate the error signal ES in the example depicted in FIG. 1, thefeedback signal path 140 comprises a subtractor 180 which is coupled toan input of the signal processing circuit 170 and to an output of theforward signal path 130 to receive the output signal. The subtractor isfurther designed to generate the error signal ES based on a differenceof the output signal and the signal provided to the signal processingcircuit 170. In FIG. 1 this is indicated by the minus sign (−) which isused at an input of the subtractor 180 coupled to the input of thesignal processing circuit 170. In other words, the signal provided tothis inverting input of the subtractor 180 causes a sign change of 180°with respect to the signal provided to the signal processing circuit170. In contrast, the output signal OS is provided to a non-invertinginput of the subtractor 180 so that the output signal is not subjectedto a sign change of a phase shift of 180°.

The error signal generated by the subtractor 180 by, for instance,subtracting the value of the output signal OS from the value of thesignal provided to the signal processing circuit 170 is then provided toa dither signal combiner 190, to which also the dither generator 160 iscoupled. As a consequence, the dither signal combiner 190 is designed tocombine the error signal ES with a dither signal DS to provide the errorsignal ES in a dithered form, also referred to as dithered error signal,to the noise-shaping filter 150. Similarly, also the forward signal path130 comprises a dither signal combiner 200 coupled between an input andthe output of a forward signal path 130 to combine the dither signal DSwith a signal provided to the dither signal combiner 200 of the forwardsignal path 130. In the implementation depicted in FIG. 1, the signalprovided to the dither signal combiner 200 is the input signal modifiedby the feedback signal FS.

In the implementation depicted in FIG. 1, the dither signal combiner 190and the feedback signal path 140 and the dither signal combiner 200 ofthe forward signal path 130 are designed and configured to combine thedither signal having the same phase relationship. In other words, boththe dither signal combiner 190 and the dither signal combiner 200 usenominally the same phase shift to combine the dither signal DS with theerror signal ES and the modified input signal IS. This may allow thecancellation or at least a reduction of the impact of the noise causedby the dither signal onto the spectral density of the output signal OS.

To modify the input signal IS, the forward signal path 130 comprises afeedback combiner 210, which is configured to modify the input signal ISby combining the input signal IS with a feedback signal FS. To be alittle more precise, the feedback combiner 210 subtracts the feedbacksignal FS from the input signal IS as indicated by the minus sign (−)used at the input of the feedback combiner 210 to which the feedbacksignal FS from the noise-shaping filter 150 is provided. Hence, thenoise-shaping filter 150 is coupled to an inverting input of a feedbackcombiner 210, while the input signal is coupled to a non-inverting inputof the feedback combiner 210. As described before, the inverting inputof the feedback combiner 210 imposes an additional phase shift of 180°or an additional change of the sign compared to its non-inverting input.

The DTC 100 comprises, hence, a control system comprising anoise-shaping circuit 120 with a forward signal path 130 (forward part)and the feedback signal path 140 (feedback part). The quantization errorcaused by the signal processing circuit 170 is returned through thefeedback signal path 140 of the noise-shaping circuit 120 and processedby the noise-shaping filter 150. As a consequence, the input datacomprised in the input signal IS are provided by the feedback combiner210 as forward path data to the dither signal combiner 200 to which thedither sequence of the dither signal DS is added. This signal is thenprovided to the signal processing circuit 170, which causes the controlsignal CS provided to the DTC 100 to be modified before it is providedto the DT circuit 110. Due to the influence of the quantization causedby the signal processing circuit 170, the modified control signal MCS isalso referred to as quantized DTC input.

In this example, an additive dither is introduced before thequantization to smear quantization spurs. If the dither signal DS wouldonly be added to the forward signal path 130 or the forward loop, it maybe visible as an additive noise level in the resulting spectrum. Forexample, if the dither signal is independent of the frequency andcomprises identically distributed random numbers, a flat noise level inthe spectral output may eventually be observed.

However, by adding the dither signal DS also to the feedback signal path140, the remaining error of the noise shaper input to the analog outputmay under ideal circumstances be restored. As a consequence, it may bepossible to regain the original spectral response of the noise-shapingcircuit 120. An example of the dithering method for a DTC-based receiversystem is depicted in FIG. 2.

FIG. 2 shows three curves indicating a DTC-based receiver (RX) outputspectrum. On the ordinate, the power of the spectral distribution (PSD)is shown in units of dBc/Hz, while the abscissa shows a frequency axistaking a frequency offset of a carrier at a frequency of 1995.7168 MHzinto account. To be a little more specific, a first spectrum 220illustrates the performance of a DTC 100 without the dither generator160 generating a dither signal DS. In other words, the first spectrum220 illustrates an output spectrum of a conventional DTC 100 whichcomprises a regular distribution of quantization spurs 230, some ofwhich are marked with the reference sign 230. Depending on theimplementation, these spurs, which may, for instance, be caused by thefinite quantization of the DTC circuit 110, may negatively influence theperformance of a system comprising the DTC 100. By adding a dithersignal DS only to the forward signal path 130, the second spectrum 240may result. Due to the additional dithering, the noise level is raisedcompared to the first spectrum 220, although the spurs 230 are no longervisible. However, in the frequency range 250, the second spectrum 240exceeds a threshold or a receiver mask 260, which comprises in thefrequency range 250 a steep edge. In the example depicted in FIG. 2,this edge in the frequency range 250 is caused by the duplex distanceor, in other words, by the frequency used for the transmitter comparedto the frequency of the carrier 270 used for receiving. In the example,the carrier 270 is located due to the compensation of the offset on theabscissa at a frequency of 0 MHz. The duplex distance in the exampledepicted is approximately 180 to 200 MHz. Hence, the additive ditherprovided only to the forward signal path 130 causes in this situation araised level in the frequency range 250, which may be reduced or evenregained due to applying the proposed method as indicated, for instance,in FIG. 1.

To illustrate this further, FIG. 2 furthermore shows a third spectrum280, which approximately corresponds to the first spectrum 220 up to andincluding the frequency range 250. However, the third spectrum does notshow the quantization spurs 230 of the first spectrum 220. Nevertheless,the noise level is slightly elevated in the frequency range up to andincluding the frequency range 250 compared to the first spectrum 220.However, in contrast to the second spectrum 240, the mask 260 is notexceeded even in the frequency range 250.

As a consequence, FIG. 2 illustrates that a noise-shaping circuit 120implemented, for instance, in a DTC 100 may be capable of improving anoverall noise performance of a system comprising such a DTC 100according to an example, by, for instance, removing the quantizationspurs 230 without causing the adverse effects in the frequency range 250as indicated by the second spectrum 240. However, in other examples,different design goals and different effects may be observed, which mayor may not improve the overall noise performance. In other words, FIG. 2merely illustrates an example where a DTC 100 according to an examplemay be implemented.

Before further examples of systems comprising a noise-shaping circuit120 according to an example will be presented, an example of a dithergenerator 160 will be described in more detail below. As outlinedbefore, the dither generator 160 may be capable of generating the dithersignal DS with different spectral densities. Depending on the differentspectral densities to be used, using different implementations for thedither generator 160 may be interesting.

FIG. 3 shows a block diagram of a dither generator 160. The dithergenerator 160 may, for instance, comprise a random number generator 290,which may produce true random numbers on the basis of which the dithersignal DS may then be generated. A random number generator isspecifically designed to generator true random numbers. It may, forinstance, comprise a circuit element or the like, which is subjected totrue random processes caused, for instance by physical or chemicalprocesses. For instance, the circuit element may be based on variationsof electronic devices such as thermal noise of a resistor, radioactivedecaying processes or the like. As a consequence, a sequence of randomnumbers generated by the random number generator 290 isnon-deterministic.

The dither generator 160 may additionally or alternatively comprise oneor more sources of pseudo-random numbers, which are at least to someextent deterministically determined. For instance, the dither generator160 may comprise a pseudo-random number generator 300, which maycalculate, for instance, based on an dither input signal DIS a sequenceof numbers, which resemble in terms of their statistical distribution atleast to some extend random numbers. Nevertheless the pseudo-randomnumbers generated by the pseudo-random number generator 300 aredeterministically determined and, hence, are not true random numbers.Pseudo-random numbers may, for instance, be calculated using recursivefunctions or the like. Often, pseudo-random number generators 300require a seat value or another starting vector, which may be providedto the pseudo-random number generator 300 via the dither input signalDIS.

Depending on the implementation, a dither generator 160 may alsocomprise a look-up table 310, which may, for instance, comprise asequence of pseudo-random numbers on the basis of which the dithersignal DS may then be generated. Depending on the implementation, astarting index or starting value may be chosen, for instance, byproviding the dither generator 160 with an appropriate value comprisedin the dither input signal DIS to name just one example.

Irrespective of the question as to whether a true random numbergenerator 290, a pseudo-random number generator 300 or a look-up table310 is employed, all these components may generate random numbers orpseudo-random numbers. Based on the random numbers or pseudo-randomnumbers provided by these components, the dither generator 160 mayoptionally internally or as the dither signal DS generate a randomsignal or a pseudo-random signal, respectively. The random signal or apseudo-random signal may then comprise one or more random numbers orpseudo-random numbers encoded in the respective signal. The randomsignal or pseudo-random signal may, for instance, be generated inresponse to a clock signal provided to an input 320. Hence, the dithergenerator 160 may be capable of generating the dither signal DS directlyor indirectly based at least on one of a random signal, a pseudo-randomsignal and a dither input signal DIS.

Optionally, the dither generator 160 may comprise a processing circuit330 to process the random signal or pseudo-random signal generated bythe components 290, 300, 310 mentioned before. For instance, theprocessing circuit 330 may high-pass filter the respective signal andgenerate the dither signal DS as a high-pass filtered random orpseudo-random signal. For instance, such a high high-pass filtering maybe implemented by differentiating the random signal or pseudo-randomsignal provided by the previously-mentioned components 290, 300, 310.However, the processing circuit 330 may also modify a distribution ofthe values provided by the previously-mentioned components, forinstance, based on the dither input signal DIS. For instance, byredistributing the values in terms of their statistical probability orby re-quantizing the respective values or signals, it may be possible toadapt the dither generator 160 and, as a consequence, the statisticaldistribution of the dither signal DS to different modes of operation ofthe noise-shaping circuit 120.

This optional implementation along with the previously-mentionedoptional implementations represent some examples of how the dithergenerator 160 may be capable of generating the dither signal DScomprising, for instance, a spectrum density depending on the ditherinput signal DIS.

It should be noted, however, that the question as to whether the dithergenerator 160 employs a random number generator 290, a pseudo-randomnumber generator 300 or a look-up table 310 may be independent from thequestion of the spectral distribution of the values. In the case of atrue random number generator 290, the underlying physical or chemicalprocess may determine or at least influence the spectral distribution ofthe values. In the case of a pseudo-random number generator 300 and alook-up table 310, the system designers may influence the spectraldistribution of the values and, hence, the spectral density of theresulting pseudo-random signals more freely.

FIG. 4 shows a block diagram of an example of a frequency synthesizer400 according to an example, which comprises a reference oscillatorcircuit 410 and at least one DTC 100 according to an example asdescribed before. To be a little more specific, in the example depictedin FIG. 4, the frequency synthesizer 400 comprises a plurality of DTCs100-1, 100-2, . . . , according to an example. Each of the DTCs 100 iscoupled to the reference oscillator circuit 410 to receive the same,common oscillating signal generated by the reference oscillator circuit410. As described before, each of the DTCs 100 is designed to provide alocal oscillator signal LO1, LO2, . . . , in response to a controlsignal CS1, CS2, . . . , respectively, based on the oscillating signalprovided by the reference oscillator circuit 410. This may allow thegeneration of multiple local oscillator signals LO1, LO2, . . . , basedon a single reference oscillator circuit 410 to which all DTCs 100 arecoupled.

For instance, the reference oscillator circuit 410 may comprise aphase-locked loop 420 (PLL) which may, for instance, be implemented as adigital PLL 420 (DPLL). The PLL 420 is coupled to a controllableoscillator 430 which generates at an output the oscillating signal forall of the DTCs 100. The output of the controllable oscillator 430 isfed back to the PLL 420, closing the phase-locked loop.

The controllable oscillator 430 may, for instance, comprise or beimplemented as a voltage-controlled oscillator (VCO) and/or as adigitally controlled oscillator (DCO). As a consequence, thecontrollable oscillator 430 may comprise an inductance or anothermagnetically active component 440, which is indicated in FIG. 4 by adotted rectangle.

By implementing a frequency synthesizer 400 comprising a plurality ofDTCs 100 and only a single reference oscillator circuit 410 comprisingan inductance or another magnetically active compound 440, it may notonly be possible to save chip area in the case of an integrated circuit,it may also be possible to reduce or even prevent magnetic interactionsbetween different reference oscillator circuits 410. As a consequence,it may be possible to improve the performance of a frequency synthesizer400, for instance, by providing more stable local oscillator signalsLO1, LO2, . . . . The DTC-based local oscillator generation depicted inFIG. 4 may be employed, for instance, for carrier aggregation (CA).

A DTC-based architecture as shown in FIG. 4 may, hence, be used forlocal oscillator signal generation using a smaller area in the case ofan implementation comprising an integrated circuit. Such animplementation may, for instance, comprise a substrate comprising thepreviously-mentioned circuits including, for instance, the referencefrequency synthesizer 400, the DTC 100 or other components describedabove and below. By using a system based on an integrated circuit, itmay be possible to use examples for instance, in high volumearchitectures such as computer system architectures in a wide sense,high volume interfaces employing corresponding devices and associatedmanufacturing processes including, for instance, thin film manufacturingprocesses and/or semiconductor manufacturing processes.

As the previous description has shown, using a noise-shaping circuit 120according to an example may, for instance, allow smearing quantizationspurs by dithering in a noise shaper for a DTC circuit 110. However,such a noise-shaper or noise-shaping circuit 120 based on dithering isby far not restricted to be applied to DTCs 100 or to the field ofcellular transceivers, Wi-Fi implementations or the like. Anoise-shaping circuit 120 may, for instance, be used along with afrequency-dependent dither level or spectral distribution to produce adistinct spectral response suitable for many applications. Ditheringalong with the described noise-shaping technique can in principle beused in all technical fields in which signals and data are processed.For instance, as will be shown in the next example, a noise-shapingcircuit may be used in every quantized system. A local oscillatorgeneration based on a DTC system may allow implementing an architecture,which can remove several PLLs 420 and/or one or more controllableoscillators 430 on a single chip or substrate.

Examples also comprise a transmitter 500, a receiver 510 or atransceiver 520 comprising a frequency synthesizer 400 as describedbefore. A simplified block diagram of a transmitter 500, a receiver 510or a transceiver 520 is depicted in FIG. 5. The transmitter 500,receiver 510 or transceiver 520 may further comprise one or more mixercircuits 530 to process the local oscillator signals LO provided by thefrequency synthesizer 400. Depending on the number of local oscillatorsignals LO provided by the frequency synthesizer 400, the transmitter500, the receiver 510 or the transceiver 520 may comprise acorresponding number of mixer circuits 530 to process the localoscillator signals LO independently of one another. The mixer circuits530 may be coupled to the DTC 100 or the DTC circuits 110 to receive theprocess oscillating signals of the DTCs 100 or the DTC circuits 110 asrespective local oscillator signals LO.

Depending on the implementation, the transmitter 500, the receiver 510or the transceiver 520 may further comprise at least one of an antenna540 or, for instance in the case of an implementation as an integratedcircuit, a terminal 550 coupled to the mixer circuit 530 and configuredto couple the antenna 540 to the mixer circuit 530. Depending on theimplementation, for instance, on the number of mixer circuits 530 andthe application, the transmitter 500, the receiver 510 or thetransceiver 520 may comprise one or more antennas 540 and/or terminals550 to allow antennas 540 to be coupled to the respective mixer circuits530. However, in case one terminal 550 or one antenna 540 is capable oftransmitting or receiving signals corresponding to more than just onefrequency of the local oscillator signals, the transmitter 500, thereceiver 510 or the transceiver 520 may comprise one or more overlaycircuits to allow the outputs of different mixer circuits 530 to becoupled to one terminal 550 or one antenna 540. For instance, to namejust one example, all mixer circuits 530 may be coupled via acorresponding overlay circuit to a single terminal 550 or a singleantenna 540.

However, as indicated before, examples are by far not limited to thegeneration of local oscillator signals or radio-based transmissiontechnology. To illustrate briefly a further example, FIG. 6 shows ablock diagram of an analog-to-digital converter 600 (ADC). The ADC 600comprises an analog-to-digital converter circuit 610 (ADC circuit),which is configured to receive an analog signal AS and to generate aquantized and sampled signal. The ADC 600 further comprises anoise-shaping circuit 120 as described before which is coupled to theADC circuit 610 to receive the quantized and sampled signal as the inputsignal IS. The noise-shaping circuit 120 may comprise, as previouslydescribed, a signal processing circuit 170 (not shown in FIG. 6)configured to at least one of re-quantizing the input signal IS,reducing the number of different values the output signal OS can acquirewith respect to the number of different values of a signal provided tothe signal processing circuit 170, reducing the number of differentvalues the output signal OS can acquire with respect to the number ofdifferent values of the input signal IS provided to the noise-shapingcircuit 120, and fully or at least partially compensating anon-linearity of the ADC circuit 610. As a consequence of all theseoperations the signal processing circuit 170 may perform, a change ofthe quantization of the input signal with respect to the output signalmay occur. As a consequence, employing a noise-shaping circuit 120according to an example may improve an overall noise performance of theADC 600.

FIG. 7 shows a block diagram of a digital-to-analog converter 700 (DAC).The DAC 700 comprises a digital-to-analog converter circuit 710 (DACcircuit), which is configured to receive a digital signal and togenerate an analog signal based on the received digital signal. The DAC700 further comprises a noise-shaping circuit 120 as described before,which is coupled to an input of the DAC circuit 710. For instance, thenoise-shaping circuit 120 may provide the output signal OS to the inputof the DAC circuit 710. As described before, the noise-shaping circuit120 generates the output signal OS based on the input signal IS, whichmay be digital signal as described before.

The DAC circuit 710 may optionally comprise digital processing circuitslike an interpolator and/or a sigma-delta modulator. Additionally oralternatively, the DAC 700 may further comprise a quantization circuit720, which may be configured to requantize the digital signal. The DAC700 may further comprise an optional active and/or passive analogprocessing circuit 730 such as filter circuits, amplifiers or the like.

Noise may arise from the optional digital processing circuits of the DACcircuit 710, the quantization circuit 720 and/or the generation of theanalog signal AS by the DAC circuit 710. Noise may also arise from theoptional analog processing circuit 730. The noise shaping circuit 120may comprise a signal processing circuit 170 configured to at least oneof re-quantizing the input signal IS, reducing the number of differentvalues the output signal OS can acquire with respect to the number ofdifferent values of the signal provided to the signal processing circuit170, reducing the number of different values the output signal OS canacquire with respect to the number of different values of the inputsignal IS provided to the noise shaping circuit 120, and at leastpartially compensating a non-linearity or a mismatch causing the noiseof the digital-to-analog converter 700 and its components. As aconsequence, an overall noise performance may be positively influencedby implementing the noise-shaping circuit 120 according to an example asoutlined before.

FIG. 8 shows a flowchart of a method for shaping noise in an inputsignal. In a process P100 using a dither generator 160, a dither signalDS is generated. In a process P110 an output signal OS based on theinput signal IS is generated in a forward signal path 130. In a processP120 using a feedback signal path 140, a feedback signal FS is fed backbased on the output signal OS to the forward signal path 130. Moreover,in a process P130, the dither signal DS is coupled into the forwardsignal path 130 to modify the input signal IS and into the feedbacksignal path 140.

Naturally, the processes are by far not required to be performed in theindicated order of FIG. 8. The processes may be performed in anarbitrary order, timely overlapping or even simultaneously. Naturally,the processes may also be performed several times or in a loop.

In the following examples pertain to further examples.

Example 1 is a noise shaping circuit comprising a forward signal pathconfigured to generate an output signal based on an input signal, afeedback signal path configured to feed back a feedback signal based onthe output signal to the forward signal path, and a dither generatorconfigured to generate a dither signal and to couple the dither signalinto the forward signal path to modify the input signal and into thefeedback signal path.

In example 2, the subject matter of example 1 may optionally include thefeedback signal path comprising a noise shaping filter configured togenerate the feedback signal based on an error signal and to provide thefeedback signal to the forward signal path, the error signal indicatinga difference of the output signal with respect to an intended value.

In example 3, the subject matter of example 2 may optionally include theforward signal path further comprising a signal processing circuitconfigured to generate the output signal based on the input signalmodified by the dither signal.

In example 4, the subject matter of example 3 may optionally include thefeedback signal path comprising a subtractor coupled to an input of thesignal processing circuit and an output of the forward signal path toreceive the output signal and configured to generate the error signalbased on a difference of the output signal and the signal provided tothe signal processing circuit.

In example 5, the subject matter of any of the examples 3 or 4 mayoptionally include the signal processing circuit comprising aquantization circuit configured to modify a value of the signal providedto the quantization circuit.

In example 6, the subject matter of any of the examples 3 to 5 mayoptionally include the signal processing circuit being configured to atleast one of re-quantizing the signal provided to the signal processingcircuit, reducing the number of different values the output signal canacquire with respect to the number of different values of the signalprovided to the signal processing circuit and at least partiallycompensating a non-linearity of a component coupled to the noise shapingcircuit.

In example 7, the subject matter of any of the examples 2 to 6 mayoptionally include the feedback signal path comprising a dither signalcombiner configured to combine the error signal with the dither signalto provide a dithered error signal to the noise shaping filter.

In example 8, the subject matter of example 7 may optionally include theforward signal path comprising a dither signal combiner coupled betweenan input and an output of the forward signal path to combine the dithersignal with the signal provided to the dither signal combiner of theforward signal path.

In example 9, the subject matter of example 8 may optionally include thedither signal combiner of the feedback signal path and the dither signalcombiner of the forward signal path being configured to combine thedither signal having the same phase relationship.

In example 10, the subject matter of any of the examples 1 to 9 mayoptionally include the noise shaping circuit being a digital noiseshaping circuit, and wherein the forward signal path, the feedbacksignal path and the dither generator are configured to receive, processand provide signals comprising a sequence of digital values.

In example 11, the subject matter of any of the examples 1 to 10 mayoptionally include the forward signal path comprising a feedbackcombiner configured to modify the input signal by combing the inputsignal with the feedback signal.

In example 12, the subject matter of example 11 may optionally includethe feedback combiner being configured to subtract the feedback signalfrom the input signal.

In example 13, the subject matter of any of the examples 1 to 12 mayoptionally include the dither generator being configured to generate thedither signal based at least on one of a random signal, a pseudo-randomsignal and a dither input signal.

In example 14, the subject matter of example 13 may optionally includethe dither generator being configured to generate the dither signalcomprising a spectral density depending on the dither input signal.

In example 15, the subject matter of any of the examples 1 to 14 mayoptionally include the dither generator being configured to generate thedither signal comprising at least one of a white noise spectral density,a pink-noise spectral density, a Brownian-noise spectral density and ahigh-pass filtered white-noise spectral density.

In example 16, the subject matter of any of the examples 1 to 15 mayoptionally include the dither generator comprising at least one of arandom number generator, a pseudo-random number generator and alook-up-table to generate a random signal or a pseudo-random signal.

In example 17, the subject matter of example 16 may optionally includethe dither generator further comprising a processing circuit configuredto process the random signal or the pseudo-random signal.

In example 18, the subject matter of example 17 may optionally includethe processing circuit of the dither generator being configured to atleast one of high-pass filtering the random signal or the pseudo-randomsignal, differentiating the random signal or the pseudo-random signaland modifying a distribution of values of the random signal or thepseudo-random signal based on a dither input signal.

Example 19 is a digital-to-time converter comprising a noise shapingcircuit according to any of the examples 1 to 18, wherein the noiseshaping circuit is configured to receive a control signal as the inputsignal, and a digital-to-time converter circuit coupled to an output ofthe noise shaping circuit to receive the output signal from the noiseshaping circuit as a modified control signal, wherein thedigital-to-time converter circuit is configured to generate a processedoscillating signal by delaying a oscillating signal in response to themodified control signal.

In example 20, the subject matter of example 19 may optionally includethe noise shaping circuit comprising a signal processing circuitconfigured to at least one of reducing a number of different states ofthe output signal compared to the signal provided to the signalprocessing circuit and compensating a non-linearity of thedigital-to-time converter circuit fully or at least partially.

In example 21, the subject matter of any of the examples 19 or 20 mayoptionally include the digital-to-time converter being a digitaldigital-to-time converter.

Example 22 is an analog-to-digital converter comprising ananalog-to-digital converter circuit configured to receive an analogsignal and to generate a quantized and sampled signal, and a noiseshaping circuit according to any of the examples 1 to 18 coupled to theanalog-to-digital converter circuit to receive the quantized and sampledsignal as the input signal.

In example 23, the subject matter of example 22 may optionally includethe noise shaping circuit comprising a signal processing circuitconfigured to at least one of re-quantizing the input signal, reducingthe number of different values the output signal can acquire withrespect to the number of different values of the signal provided to thesignal processing circuit, reducing the number of different values theoutput signal can acquire with respect to the number of different valuesof the input signal provided to the noise shaping circuit, and at leastpartially compensating a non-linearity of the analog-to-digitalconverter circuit.

Example 24 is a frequency synthesizer comprising a reference oscillatorcircuit, and a digital-to-time converter according to any of theexamples 19 to 21, wherein the reference oscillator circuit is coupledto the digital-to-time converter circuit and configured to provide theoscillating signal to the digital-to-time converter, wherein thedigital-to-time converter circuit is configured to provide the processedoscillating signal as a local oscillator signal.

In example 25, the subject matter of example 24 may optionally include aplurality of digital-to-time converters according to any of the examples19 to 21, wherein each of the digital-to-time converter circuits iscoupled to the reference oscillator circuit to receive the oscillatingsignal generated by the reference oscillator circuit.

In example 26, the subject matter of example 25 may optionally includethe local oscillator circuit comprising a single reference oscillatorcircuit, which is coupled to all digital-to-time converter circuits ofthe plurality of digital-to-time converters to provide thedigital-to-time converter circuits with the same oscillating signal.

In example 27, the subject matter of any of the examples 24 to 26 mayoptionally include the reference oscillator circuit comprising aninductance or another magnetically active component.

Example 28 is a transmitter, a receiver or a transceiver comprising afrequency synthesizer according to any of the examples 24 to 27.

In example 29, the subject matter of example 28 may optionally include amixer circuit coupled to the digital-to-time converter to receive theprocessed oscillating signal of the digital-to-time converter as thelocal oscillator signal.

In example 30, the subject matter of example 29 may optionally includeat least one of an antenna coupled to the mixer circuit and a terminalcoupled to the mixer circuit and configured to couple an antenna to themixer circuit.

Example 31 is a digital-to-analog converter comprising a digital-toanalog converter circuit configured to receive a digital signal and togenerate an analog signal, and a noise shaping circuit according to anyof the examples 1 to 18 coupled to the digital-to-analog convertercircuit to receive an input signal and to generate the output signal asthe digital signal for the digital-to analog converter circuit.

In example 32, the subject matter of example 31 may optionally includethe noise shaping circuit comprising a signal processing circuitconfigured to at least one of re-quantizing the input signal, reducingthe number of different values the output signal can acquire withrespect to the number of different values of the signal provided to thesignal processing circuit, reducing the number of different values theoutput signal can acquire with respect to the number of different valuesof the input signal provided to the noise shaping circuit, at leastpartially compensating a non-linearity of the digital-to-analogconverter and at least partially compensating a mismatch of thedigital-to-analog converter.

Example 33 is a method for shaping noise in an input signal, the methodcomprising generating, using a dither generator, a dither signal,generating an output signal based on the input signal in a forwardsignal path, feeding back, using a feedback signal path, a feedbacksignal based on the output signal to the forward signal path andcoupling the dither signal into the forward signal path to modify theinput signal and into the feedback signal path.

In example 34, the subject matter of example 33 may optionally includefeeding back the feedback signal comprising generating the feedbacksignal based on an error signal and providing the feedback signal to theforward signal path by a noise shaping filter, wherein the error signalis indicating a difference of the output signal with respect to anintended value.

In example 35, the subject matter of example 34 may optionally includegenerating the output signal comprising generating the output signal bysignal processing based on the input signal modified by the dithersignal.

In example 36, the subject matter of example 35 may optionally includefeeding back the feedback signal comprising subtracting a signal priorto signal processing and the output signal of the forward signal pathand generating the error signal based on a difference of the outputsignal and the signal prior to signal processing.

In example 37, the subject matter of any of the examples 35 or 36 mayoptionally include the signal processing comprising modifying a value ofthe signal prior to modifying.

In example 38, the subject matter of any of the examples 35 to 37 mayoptionally include the signal processing comprising at least one ofre-quantizing the signal to be processed, reducing the number ofdifferent values the output signal can acquire with respect to thenumber of different values of the signal prior to signal processing andat least partially compensating a non-linearity of a component.

In example 39, the subject matter of any of the examples 34 to 38 mayoptionally include coupling the dither signal into the feedback signalpath comprising combining the error signal with the dither signal toprovide a dithered error signal and providing the dithered error signalto the noise shaping filter.

In example 40, the subject matter of example 39 may optionally includecoupling the dither signal into the forward signal path and into thefeedback signal path comprising combining the dither signal having thesame phase relationship.

In example 41, the subject matter of any of the examples 33 to 40 mayoptionally include the method being digitally performed, and wherein thesignals comprise a sequence of digital values.

In example 42, the subject matter of any of the examples 31 to 41 mayoptionally include feeding back the feedback signal comprising modifyingthe input signal by combing the input signal with the feedback signal.

In example 43, the subject matter of example 42 may optionally includecombining the input signal with the feedback signal comprisingsubtracting the feedback signal from the input signal to modify theinput signal.

In example 44, the subject matter of any of the examples 33 to 43 mayoptionally include generating the dither signal comprising generatingthe dither signal based at least on one of a random signal, apseudo-random signal and a dither input signal.

In example 45, the subject matter of example 44 may optionally includegenerating the dither signal comprising generating the dither signalcomprising a spectral density depending on the dither input signal.

In example 46, the subject matter of any of the examples 33 to 45 mayoptionally include generating the dither signal comprising generatingthe dither signal comprising a white noise spectral density, apink-noise spectral density, a Brownian noise shape or a high-passfiltered white noise spectral density.

Example 47 is a machine readable storage medium including program code,when executed, to cause a machine to perform the method of any one ofexamples 33 to 46.

Example 48 is a machine readable storage including machine readableinstructions, when executed, to implement a method or realize anapparatus as described in any pending example.

Example 49 is a computer program having a program code for performingany of the methods of examples 33 to 46, when the computer program isexecuted on a computer or processor.

Example 50 is a means for shaping the noise in an input signal, themeans comprising a means for generating a dither signal, a means forgenerating an output signal based on the input signal in a forwardsignal path, a means for feeding back, using a feedback signal path, afeedback signal based on the output signal to the forward signal path,and a means for coupling the dither signal into the forward signal pathto modify the input signal and into the feedback signal path.

Employing a noise shaping circuit according to an example may improve anoverall noise performance.

Examples may, therefore, provide a computer program having a programcode for performing one of the above methods, when the computer programis executed on a computer or processor. A person of skill in the artwould readily recognize that steps of various above-described methodsmay be performed by programmed computers. Herein, some examples are alsointended to cover program storage devices, e.g., digital data storagemedia, which are machine or computer readable and encodemachine-executable or computer-executable programs of instructions,wherein the instructions perform some or all of the acts of theabove-described methods. The program storage devices may be, e.g.,digital memories, magnetic storage media such as magnetic disks andmagnetic tapes, hard drives, or optically readable digital data storagemedia. The examples are also intended to cover computers programmed toperform the acts of the above-described methods or (field) programmablelogic arrays ((F)PLAs) or (field) programmable gate arrays ((F)PGAs),programmed to perform the acts of the above-described methods.

The description and drawings merely illustrate the principles of thedisclosure. It will thus be appreciated that those skilled in the artwill be able to devise various arrangements that, although notexplicitly described or shown herein, embody the principles of thedisclosure and are included within its spirit and scope. Furthermore,all examples recited herein are principally intended expressly to beonly for pedagogical purposes to aid the reader in understanding theprinciples of the disclosure and the concepts contributed by theinventor(s) to furthering the art, and are to be construed as beingwithout limitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andexamples of the disclosure, as well as specific examples thereof, areintended to encompass equivalents thereof.

Functional blocks denoted as “means for . . . ” (performing a certainfunction) shall be understood as functional blocks comprising circuitrythat is configured to perform a certain function, respectively. Hence, a“means for s.th.” may as well be understood as a “means configured to orsuited for s.th.”. A means configured to perform a certain functiondoes, hence, not imply that such means necessarily is performing thefunction (at a given time instant).

Functions of various elements shown in the figures, including anyfunctional blocks labeled as “means”, “means for providing a sensorsignal”, “means for generating a transmit signal.”, etc., may beprovided through the use of dedicated hardware, such as “a signalprovider”, “a signal processing unit”, “a processor”, “a controller”,etc. as well as hardware capable of executing software in associationwith appropriate software. Moreover, any entity described herein as“means”, may correspond to or be implemented as “one or more modules”,“one or more devices”, “one or more units”, etc. When provided by aprocessor, the functions may be provided by a single dedicatedprocessor, by a single shared processor, or by a plurality of individualprocessors, some of which may be shared. Moreover, explicit use of theterm “processor” or “controller” should not be construed to referexclusively to hardware capable of executing software, and mayimplicitly include, without limitation, digital signal processor (DSP)hardware, network processor, application specific integrated circuit(ASIC), field programmable gate array (FPGA), read only memory (ROM) forstoring software, random access memory (RAM), and non-volatile storage.Other hardware, conventional and/or custom, may also be included.

It should be appreciated by those skilled in the art that any blockdiagrams herein represent conceptual views of illustrative circuitryembodying the principles of the disclosure. Similarly, it will beappreciated that any flow charts, flow diagrams, state transitiondiagrams, pseudo code, and the like represent various processes whichmay be substantially represented in computer readable medium and soexecuted by a computer or processor, whether or not such computer orprocessor is explicitly shown.

Furthermore, the following claims are hereby incorporated into theDetailed Description, where each claim may stand on its own as aseparate example. While each claim may stand on its own as a separateexample, it is to be noted that—although a dependent claim may refer inthe claims to a specific combination with one or more other claims—otherexamples may also include a combination of the dependent claim with thesubject matter of each other dependent or independent claim. Suchcombinations are proposed herein unless it is stated that a specificcombination is not intended. Furthermore, it is intended to include alsofeatures of a claim to any other independent claim even if this claim isnot directly made dependent to the independent claim.

It is further to be noted that methods disclosed in the specification orin the claims may be implemented by a device having means for performingeach of the respective acts of these methods.

Further, it is to be understood that the disclosure of multiple acts orfunctions disclosed in the specification or claims may not be construedas to be within the specific order. Therefore, the disclosure ofmultiple acts or functions will not limit these to a particular orderunless such acts or functions are not interchangeable for technicalreasons. Furthermore, in some examples a single act may include or maybe broken into multiple sub acts. Such sub-acts or sub-processes may beincluded and be part of such a single act or process, unless explicitlyexcluded.

The invention claimed is:
 1. A noise shaping circuit comprising: aforward signal path configured to generate an output signal based on aninput signal; a feedback signal path configured to feed back a feedbacksignal based on the output signal to the forward signal path; and adither generator configured to generate a dither signal and to couplethe dither signal into the forward signal path to modify the inputsignal and into the feedback signal path, wherein the feedback signalpath comprises a noise shaping filter configured to generate thefeedback signal based on an error signal and to provide the feedbacksignal to the forward signal path, the error signal indicating adifference of the output signal with respect to an intended value, andwherein the feedback signal path comprises a dither signal combinerconfigured to combine the error signal with the dither signal to providea dithered error signal to the noise shaping filter.
 2. The noiseshaping circuit according to claim 1, wherein the forward signal pathfurther comprises a signal processing circuit configured to generate theoutput signal based on the input signal modified by the dither signal.3. The noise shaping circuit according to claim 2, wherein the feedbacksignal path comprises a subtractor coupled to an input of the signalprocessing circuit and an output of the forward signal path to receivethe output signal and configured to generate the error signal based on adifference of the output signal and the signal provided to the signalprocessing circuit.
 4. The noise shaping circuit according to claim 2,wherein the signal processing circuit comprises a quantization circuitconfigured to modify a value of the signal provided to the quantizationcircuit.
 5. The noise shaping circuit according to claim 2, wherein thesignal processing circuit is configured to at least one of re-quantizingthe signal provided to the signal processing circuit, reducing thenumber of different values the output signal can acquire with respect tothe number of different values of the signal provided to the signalprocessing circuit and at least partially compensating a non-linearityof a component coupled to the noise shaping circuit.
 6. The noiseshaping circuit according to claim 1, wherein the forward signal pathcomprises a dither signal combiner coupled between an input and anoutput of the forward signal path to combine the dither signal with thesignal provided to the dither signal combiner of the forward signalpath.
 7. The noise shaping circuit according to claim 6, wherein thedither signal combiner of the feedback signal path and the dither signalcombiner of the forward signal path are configured to combine the dithersignal having the same phase relationship.
 8. The noise shaping circuitaccording to claim 1, wherein the noise shaping circuit is a digitalnoise shaping circuit, and wherein the forward signal path, the feedbacksignal path and the dither generator are configured to receive, processand provide signals comprising a sequence of digital values.
 9. Thenoise shaping circuit according to claim 1, wherein the dither generatoris configured to generate the dither signal based at least on one of arandom signal, a pseudo-random signal and a dither input signal.
 10. Thenoise shaping circuit according claim 9, wherein the dither generator isconfigured to generate the dither signal comprising a spectral densitydepending on the dither input signal.
 11. The noise shaping circuitaccording claim 1, wherein the dither generator is configured togenerate the dither signal comprising at least one of a white noisespectral density, a pink-noise spectral density, a Brownian-noisespectral density and a high-pass filtered white-noise spectral density.12. The noise shaping circuit according to claim 1, wherein the dithergenerator comprises at least one of a random number generator, apseudo-random number generator and a look-up-table to generate a randomsignal or a pseudo-random signal.
 13. The noise shaping circuitaccording to claim 12, wherein the dither generator further comprises aprocessing circuit configured to process the random signal or thepseudo-random signal.
 14. The noise shaping circuit according to claim13, wherein the processing circuit of the dither generator is configuredto at least one of high-pass filtering the random signal or thepseudo-random signal, differentiating the random signal or thepseudo-random signal and modifying a distribution of values of therandom signal or the pseudo-random signal based on a dither inputsignal.
 15. A noise shaping circuit comprising: a forward signal pathconfigured to generate an output signal based on an input signal; afeedback signal path configured to feed back a feedback signal based onthe output signal to the forward signal path; and a dither generatorconfigured to generate a dither signal and to couple the dither signalinto the forward signal path to modify the input signal and into thefeedback signal path, wherein the forward signal path comprises afeedback combiner configured to modify the input signal by combing theinput signal with the feedback signal, and wherein the feedback combineris configured to subtract the feedback signal from the input signal. 16.A digital-to-time converter comprising: a noise shaping circuitcomprising a forward signal path configured to generate an output signalbased on an input signal, a feedback signal path configured to feed backa feedback signal based on the output signal to the forward signal path,and a dither generator configured to generate a dither signal and tocouple the dither signal into the forward signal path to modify theinput signal and into the feedback signal path, wherein the noiseshaping circuit is configured to receive a control signal as the inputsignal; and a digital-to-time converter circuit coupled to an output ofthe noise shaping circuit to receive the output signal from the noiseshaping circuit as a modified control signal, wherein thedigital-to-time converter circuit is configured to generate a processedoscillating signal by delaying a oscillating signal in response to themodified control signal, wherein the feedback signal path comprises adither signal combiner configured to combine the error signal with thedither signal to provide a dithered error signal to the noise shapingcircuit.
 17. The digital-to-time converter according to claim 16,wherein the noise shaping circuit comprises a signal processing circuitconfigured to at least one of reducing a number of different states ofthe output signal compared to the signal provided to the signalprocessing circuit and compensating a non-linearity of thedigital-to-time converter circuit fully or at least partially.
 18. Thedigital-to-time converter according to claim 16, wherein thedigital-to-time converter is a digital digital-to-time converter.